Connect to an AWS API via boto3 low-level client and set self.conn
to the boto3.client object
(a botocore.client.* instance). If self.conn is not None,
do nothing. This connects to the API name given by self.api_name.

Connect to an AWS API via boto3 high-level resource connection and set
self.resource_conn to the boto3.resource object
(a boto3.resources.factory.*.ServiceResource instance).
If self.resource_conn is not None,
do nothing. This connects to the API name given by self.api_name.